Process for the production of cast iron having needle-shaped crystalline structure



Aug. 12, 1958 w. RUFF 2,847,337

PROCESS FOR THE PRQDUCT'ION 0F CAST IRON HAVING NEEDLE-$HAD CRYSTALLINE STRUCTURE Filed May 2. 1956 0 0,5 ,0 z; Z0 Z5 \za 3 COIVIE YZS INVENTOR: W05??? 1? Vi?" strength.

2,847,337 Patented Aug. 12, 1958 2,847,337 PROCESS FOR THE PRODUCTION OF CAST IRON HAVING NEEDLE -SHAPED CRYSTALLINE STRUCTURE Wolfram Ruff, Frankfurt am Main, Germany, assignmto Alfred Teves, .Maschinenund Armaturenfabrik KG, Frankfurt am Main, Germany Application May 2, 1956, Serial No. 582,191 Claims priority, application Germany July 8, 1955 3 Claims. (Cl. 148-2'1.7)

This invention relates to the production of cast iron and is directed particularly to a process of the production of needle-shaped crystalline structure cast iron having superior physical characteristics.

The method of producing cast iron having a needleshaped ferrite crystal structure is known. Reference may be had, for example, to the German text Gusseisen by E. Piwowarsky, published in 1951, pages 707- 714 and 725, wherein various methods for producing such cast iron are disclosed. The structure may, for instance, be brought about by a heat treatment of perlitic cast iron; in general it is, however, preferable to arrive at the desired structure by a variation of the alloy components, especially Mo, Ni, Cu, and Cr. The amount of alloy components is so adjusted, that it will not be sufficient for obtaining a martensitic or austenitic cast iron, but will be above the amount which would lead to perlitic iron, in order to arrive at an iron of suflicient In other words, it is necessary to select the alioy component in such a manner that, with a given cooling velocity, the conversion of austenite to the desired needle structure of ferrite crystals will be brought about in the temperature range of 480-260 C.

The needle-shaped structure of the base mass has resulted in a new term acicular cast iron.

The difiiculties hitherto encountered in the production of cast iron with needle-shaped crystalline structure becomes readily apparent from the cited literature. The castings made as there described are hardly any better, as far as their mechanical strength is concerned, and as an added inconvenience, they exhibit a stronger tendency to bending. Attempts have been made to improve the strength by heating from 5 hours up, and to vary the percentage of alloy components added. The production of high quality cast iron, particularly of unalloyed cast iron having a high so-called saturation value, is still an unsolved problem.

It is accordingly the principal object of my invention to provide an improved and simplified process for the production of high grade, wear-resisting cast iron having a needle-shaped crystalline structure.

Other objects, advantages and features of the invention will be apparent from the following description of the improved process.

The invention is based on the discovery that high quality cast iron having a needle-shaped crystal structure is well possible, even with the eutectical saturation value of over 0.9, it, prior to the warm bath quenching step required for producting the needle-shaped ferrite, the iron is subjected to an especially high homogenizing temperature which is at least 120 C. above the equilibrium temperature line A of the FeCSi-diagram attached herewith.

By the term eutectical saturation (Sc) value is Percent C Percent Si 4.23

An objectionable needle-shaped crystalline structure results and therefore cast iron having high wear-resisting qualities, and otherwise good characteristics is obtained without the need of an alloying additive.

The new process herein disclosed is especially advantageous in the production of piston rings, cylinder walls, and similar machine parts.

In the following the new process will be described as applied to piston rings for example. It should, however, be understood that the examples given hereinbelow are by way of illustration and not of limitation and that many changes in the details could be made without departing from the spirit of the invention.

In the examples the piston rings are made of cast iron composed of 3.8% C, 2.5% Si, 0.4% Men, 0.2% P, balance Fe.

Example 1 The piston rings are subjected to a temperature of 925 C. for 15 minutes and thereafter quenched in a warm bath having a temperature of 425 C. in which they are held for about 4 minutes. After subsequent air cooling, the piston rings fully exhibit the desired needleshaped ferrite crystal structure.

Example 2 The piston rings of the composition as described are treated as in Example 1; they are then quenched in a warm bath having a temperature of 300 C. and thereafter annealed at a temperature of 450525 C. They are subsequently air cooled.

The needle-shaped ferrite crystal structure so obtained, besides resulting in high-wear-resisting qualities in internal combustion engines, also imparts good running characteristics to the articles made of the cast iron. In addition to the good running characteristics, piston rings produced according to the invention exhibit a greatly increased hardness, strength and elasticity as compared to ordinary grey cast iron piston rings. The chromium plating often used today on grey cast iron piston rings can be dispensed with on cast iron piston rings produced according to the invention. Moreover, piston rings produced according to the invention, because of having a high content of granular graphite, enter into strong competition with steel piston rings.

What I claim is:

1. The process of producing wear-resistant cast iron having a needle-shaped crystal structure, which comprises heat-treating iron having an eutectical saturation value of 0.9 and over, said value being determined by the formula:

Percent C Percent Si 3.2

at a temperature of at least C. above the equilibriuni temperature line of the FeCSi-equilibrium diagram, designated as A in said diagram, and then quenching the iron to a temperature ranging from 300425 C.

2. The process of producing cast iron piston rings and similar parts subjected to abrasive action when in use, which comprises forming the parts of iron having an eutectical saturation value of 0.9 and over, said value being determined by the formula:

' S0 Percent C 4 Percent Si heat-treating said parts at a temperature of at least 120 C. above the equilibrium temperature line of the FeCSiequilibrium diagram, designated as A in said diagram, holding said parts at said heat-treating temperature for =5? about 15 minutes, and then quenching the heat-treated parts to a temperature of about 425 C.

3. The process of producing cast iron piston rings and similar parts subjected to abrasive action when in use, which comprises forming the parts of iron having an eutectical saturation value of 0.9 and over, said value being determined by the formula:

Percent C Pereen1; Si 3.2

heat-treating said parts at a temperature of at l ast 129 C. above the equilibrium temperature line of the FeCSiequilibrium diagram, designated as A in said diagram, holding said parts at said heat-treating temperature for about 15 minutes, then quenching the heat-treated parts to a temperature of about 300 C. and finally annealing them at a temperature ranging from 450525 C.

References Cited in the file of this patent UNITED STATES PATENTS 2,485,760 Millis et a1. Oct. 25, 1949 OTHER REFERENCES The Iron Age, vol. 147, February 13, 1941, pages 43-46.

American Foundrymens Association, Transactions, vol. 46, July 1938-Iune 1939, pages 563-586.

Cast Metal Handbook, 1940 edition, published by 15 American Foundrymens Association, page 464. 

1. THE PROCESS OF PRODUCING WEAR-RESISTANT CAST IRON HAVING A NEEDLE-SHAPED CRYSTAL STRUCTURE, WHICH COMPRISES HEAT-TREATING IRON HAVING AN EUTECTICAL SATURATION 